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Black Diamond sewer upgrade
The Black Diamond Sewer Upgrade Project will increase capacity for 6 miles of regional sewer pipe in Black Diamond. The project will help us treat more wastewater to meet the needs of the growing Black Diamond community.
Project description
Upgrading the sewer pipe to meet Black Diamond's growth
Black Diamond is one of the fastest-growing communities in the Puget Sound region. In 1992, in collaboration with King County, the City built a regional sewer line to serve the area’s much smaller population at the time. Today, we need to upgrade the existing sewer line because it’s reaching capacity. Upgrading the sewer line may include a combination of repairing the existing pipe and installing new pipes
The project will look at options to upgrade 6 miles of sewer pipe in Black Diamond. The option we select will:
- Serve the community’s wastewater capacity needs through 2070
- Ensure reliable wastewater service to Black Diamond's homes and businesses
- Foster a healthy and resilient community with reliable wastewater infrastructure
Project update
December 2025
Lane closure on 224th Ave SE planned for December 11 and 12
King County plans to temporarily close one lane of traffic on 224th Avenue SE, between SE 300th Street and SE 297th Street, on December 11 and 12 to collect soil samples.
Crews will drill two to three holes in the ground to collect samples, then restore all work areas.
These new samples will add to the ones collected in 2024. They will help us learn more about the underground conditions. We will use this data to help design our project.
View project notice.
What’s next?
We are wrapping up the preliminary design by this year. We will continue to share more project updates with you. Please sign up for project updates to stay up-to-date on the latest project information and upcoming events.
Interested in a project briefing for your community group?
We are happy to meet with you or come to your next community event to share the latest project information and to answer questions you might have as we get closer to construction. Please contact Annie Plumley at 206-263-3203 or BDSewerUpgrade@kingcounty.gov for more information.
Previous project updates
- Your voice matters: Share your thoughts on the Black Diamond Sewer Upgrade Project, July 2025
- Wetland sampling along the regional sewer pipeline planned for April 10 through April 15, April 9, 2025
- Traffic control and lane shifts along King County pipeline planned for February 19, February 14, 2025
- Exploratory surveys for an upcoming King County project starting in your area, August 2024
Project location
Understanding site conditions and community needs
Our team is in the early stages of design for the project. During the design phase, the project team will:
- Survey the project area to understand existing conditions in Black Diamond
- Conduct geotechnical surveys to understand underground conditions
- Inform community members about the project and upcoming survey work
- Analyze design alternatives and identify a preferred option to upgrade the sewer
- Complete 30% design for the project
Working with the community
We’ll share details about specific engagement opportunities as the project progresses
We’re committed to engaging with the community during each stage of the project, and we want to make sure everyone has access to information. We welcome you to take part in the project in the following ways:
- Contact us to have a one-on-one conversation by phone, video chat, email, or in person.
- Invite us to a meeting hosted by your group or organization.
- Join our team remotely or in person at future meetings at project milestones. We will post these meetings on our website and email list once they are scheduled.
Interpretation and translation services are available to you at no cost. If you need them, please contact Annie Plumley, BDSewerUpgrade@kingcounty.gov, 206-263-3203.
Los servicios de interpretación y traducción están disponibles para usted sin costo alguno. Si los necesita, comuníquese con Annie Plumley, BDSewerUpgrade@kingcounty.gov, 206-263-3203.